Inhibition of histone deacetylase 2 increases apoptosis and p21Cip1/WAF1 expression, independent of histone deacetylase 1

Understanding the Anticancer Effects of Phytochemicals: From Molecular Docking to Anticarcinogenic Signaling

As nontraditional nutrients, the biological activity of phytochemicals have been extensively studied for their antioxidant, anti-inflammatory, and apoptosis-promoting effects in various diseases. The general anticancer benefits of phytochemicals have been demonstrated in both basic researches and clinical trials. However, researchers understanding of how phytochemicals target cancer-related signaling pathways is still in its infancy. Molecular docking simulation analyses have yielded a large amount of cellular target molecules of phytochemicals. Herein, we review the potential signaling pathways that may be involved in the phytochemical-driven cancer benefits. We expect these findings to help in the design of potential cancer treatments designed by manipulating the binding modes and sites of these plant chemicals.

Multi-functional biotinylated platinum(IV)-SAHA conjugate for tumor-targeted chemotherapy

The development of multi-functional Pt(IV) complexes as chemotherapeutic agents has gained growing attention in medical oncology. However, the design of multi-functional tumor-targeted Pt(IV) complexes with high hydrolytic stability remains challenging. Herein, we have developed a Pt(IV) prodrug conjugated with vorinostat as a multi-functional cancer therapeutic. In this design, the octahedral Pt(IV) prodrug of a DNA damaging anticancer drug cisplatin is tethered to the cancer cell targeting biotin ligand through one of the axial sites and the other axial site of the Pt(IV) center is attached to the anticancer drug vorinostat (also known as SAHA), a histone deacetylase inhibitor (HDACi) approved by the Food and Drug Administration (FDA) for treatment of cutaneous T-cell lymphoma. The designed biotinylated Pt(iv)-SAHA (Biotin-Pt(iv)-SAHA) conjugate is hydrolytically stable but reduced to Pt(II) species under intracellularly relevant conditions and concomitantly releases cisplatin and two of its axial ligands such as SAHA and biotin. The anticancer activity of the conjugate is investigated against a panel of cisplatin-sensitive human cancer cells, including cisplatin-resistant cells. Interestingly, the conjugate exhibited significantly higher cytotoxicity than the clinically approved anticancer drug cisplatin and slightly more cytotoxicity than the HDACi SAHA in all the tested cell lines. By combining the Pt(IV) prodrug of cisplatin with SAHA in the conjugate, synergistic cytotoxicity is achieved. The imaging studies revealed that the conjugate is taken up by cancer cells and shows dose-dependent cell death. The studies on our designed multi-pronged conjugate can be further optimized to enhance its efficacy, paving the way for developing a new class of clinically relevant chemotherapeutic agents.

Paeonia genus: a systematic review of active ingredients, pharmacological effects and mechanisms, and clinical applications for the treatment of cancer

The main active constituents of plants of the Paeonia genus are known to have antitumor activity. Hundreds of compounds with a wide range of pharmacological activities, including monoterpene glycosides, flavonoids, tannins, stilbenes, triterpenoids, steroids, and phenolic compounds have been isolated. Among them, monoterpenes and their glycosides, flavonoids, phenolic acids, and other constituents have been shown to have good therapeutic effects on various cancers, with the main mechanisms including the induction of apoptosis; the inhibition of tumor cell proliferation, migration, and invasion; and the modulation of immunity. In this study, many citations related to the traditional uses, phytochemical constituents, antitumor effects, and clinical applications of the Paeonia genus were retrieved from popular and widely used databases such as Web of Science, Science Direct, Google Scholar, and PubMed using different search strings. A systematic review of the antitumor constituents of the Paeonia genus and their therapeutic effects on various cancers was conducted and the mechanisms of action and pathways of these phytochemicals were summarised to provide a further basis for antitumor research.

Hydrazides as Inhibitors of Histone Deacetylases

In this Perspective, we have brought together available biological evidence on hydrazides as histone deacetylase inhibitors (HDACis) and as a distinct type of Zn-binding group (ZBG) to be reviewed for the first time in the literature. N-Alkyl hydrazides have transformed the field, providing innovative and practical chemical tools for selective and effective inhibition of specific histone deacetylase (HDAC) enzymes, in addition to the usual hydroxamic acid and o-aminoanilide ZBG-bearing HDACis. This has enabled efficient targeting of neurodegenerative diseases such as Alzheimer's disease, cancer, cardiovascular diseases, and protozoal pathologies.

Stochasticity of anticancer mechanisms underlying clinical effectiveness of vorinostat

The Food and Drug Administration (FDA) has approved vorinostat, also called Zolinza®, for its effectiveness in fighting cancer. This drug is a suberoyl-anilide hydroxamic acid belonging to the class of histone deacetylase inhibitors (HDACis). Its HDAC inhibitory potential allows it to accumulate acetylated histones. This, in turn, can restore normal gene expression in cancer cells and activate multiple signaling pathways. Experiments have proven that vorinostat induces histone acetylation and cytotoxicity in many cancer cell lines, increases the level of p21 cell cycle proteins, and enhances pro-apoptotic factors while decreasing anti-apoptotic factors. Additionally, it regulates the immune response by up-regulating programmed death-ligand 1 (PD-L1) and interferon gamma receptor 1 (IFN-γR1) expression, and can impact proteasome and/or aggresome degradation, endoplasmic reticulum function, cell cycle arrest, apoptosis, tumor microenvironment remodeling, and angiogenesis inhibition. In this study, we sought to elucidate the precise molecular mechanism by which Vorinostat inhibits HDACs. A deeper understanding of these mechanisms could improve our understanding of cancer cell abnormalities and provide new therapeutic possibilities for cancer treatment.

CDKN1A/p21 in Breast Cancer: Part of the Problem, or Part of the Solution?

Cyclin-dependent kinase inhibitor 1A (Cip1/Waf1/CDKN1A/p21) is a well-established protein, primarily recognised for its pivotal role in the cell cycle, where it induces cell cycle arrest by inhibiting the activity of cyclin-dependent kinases (CDKs). Over the years, extensive research has shed light on various additional mechanisms involving CDKN1A/p21, implicating it in processes such as apoptosis, DNA damage response (DDR), and the regulation of stem cell fate. Interestingly, p21 can function either as an oncogene or as a tumour suppressor in these contexts. Complicating matters further, the expression of CDKN1A/p21 is elevated in certain tumour types while downregulated in others. In this comprehensive review, we provide an overview of the multifaceted functions of CDKN1A/p21, present clinical data pertaining to cancer patients, and delve into potential strategies for targeting CDKN1A/p21 as a therapeutic approach to cancer. Manipulating CDKN1A/p21 shows great promise for therapy given its involvement in multiple cancer hallmarks, such as sustained cell proliferation, the renewal of cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), cell migration, and resistance to chemotherapy. Given the dual role of CDKN1A/p21 in these processes, a more in-depth understanding of its specific mechanisms of action and its regulatory network is imperative to establishing successful therapeutic interventions.

Antineoplastic activity of plant-derived compounds mediated through inhibition of histone deacetylase: a review

In the combat of treating cancer recent therapeutic approaches are focused towards enzymatic targets as they occupy a pivotal participation in the cascade of oncogenesis and malignancy. There are several enzymes that modulate the epigenetic pathways and chromatin structure related to cancer mutation. Among several epigenetic mechanisms such as methylation, phosphorylation, and sumoylation, acetylation status of histones is crucial and is governed by counteracting enzymes like histone acetyl transferase (HAT) and histone deacetylases (HDAC) which have contradictory effects on the histone acetylation. HDAC inhibition induces chromatin relaxation which forms euchromatin and thereby initiates the expression of certain transcription factors attributed with apoptosis, which are mostly correlated with the expression of the p21 gene and acetylation of H3 and H4 histones. Most of the synthetic and natural HDAC inhibitors elicit antineoplastic effect through activation of various apoptotic pathways and promoting cell cycle arrest at various phases. Due to their promising chemo preventive action and low cytotoxicity against normal host cells, bioactive substances like flavonoids, alkaloids, and polyphenolic compounds from plants have recently gained importance. Even though all bioactive compounds mentioned have an HDAC inhibitory action, some of them have a direct effect and others enhance the effects of the standard well known HDAC inhibitors. In this review, the action of plant derived compounds against histone deacetylases in a variety of in vitro cancer cell lines and in vivo animal models are articulated.

UBE4B interacts with the ITCH E3 ubiquitin ligase to induce Ku70 and c-FLIPL polyubiquitination and enhanced neuroblastoma apoptosis

Expression of the UBE4B ubiquitin ligase is strongly associated with neuroblastoma patient outcomes, but the functional roles of UBE4B in neuroblastoma pathogenesis are not known. We evaluated interactions of UBE4B with the E3 ubiquitin ligase ITCH/AIP4 and the effects of UBE4B expression on Ku70 and c-FLIPL ubiquitination and proteasomal degradation by co-immunoprecipitation and Western blots. We also evaluated the role of UBE4B in apoptosis induced by histone deacetylase (HDAC) inhibition using Western blots. UBE4B binding to ITCH was mediated by WW domains in the ITCH protein. ITCH activation led to ITCH-UBE4B complex formation and recruitment of Ku70 and c-FLIPL via ITCH WW domains, followed by Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination and proteasomal degradation. HDAC inhibition induced Ku70 acetylation, leading to release of c-FLIPL and Bax from Ku70, increased Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination via the ITCH-UBE4B complex, and induction of apoptosis. UBE4B depletion led to reduced polyubiquitination and increased levels of Ku70 and c-FLIPL and to reduced apoptosis induced by HDAC inhibition via stabilization of c-FLIPL and Ku70 and inhibition of caspase 8 activation. Our results have identified novel interactions and novel targets for UBE4B ubiquitin ligase activity and a direct role for the ITCH-UBE4B complex in responses of neuroblastoma cells to HDAC inhibition, suggesting that the ITCH-UBE4B complex plays a critical role in responses of neuroblastoma to therapy and identifying a potential mechanism underlying the association of UBE4B expression with neuroblastoma patient outcomes.

Emerging Role of Epigenetic Modifiers in Breast Cancer Pathogenesis and Therapeutic Response

Breast cancer pathogenesis, treatment, and patient outcomes are shaped by tumor-intrinsic genomic alterations that divide breast tumors into molecular subtypes. These molecular subtypes often dictate viable therapeutic interventions and, ultimately, patient outcomes. However, heterogeneity in therapeutic response may be a result of underlying epigenetic features that may further stratify breast cancer patient outcomes. In this review, we examine non-genetic mechanisms that drive functional changes to chromatin in breast cancer to contribute to cell and tumor fitness and highlight how epigenetic activity may inform the therapeutic response. We conclude by providing perspectives on the future of therapeutic targeting of epigenetic enzymes, an approach that holds untapped potential to improve breast cancer patient outcomes.

Epigenetic Regulation of Leukocyte Inflammatory Mediator Production Dictates Staphylococcus aureus Craniotomy Infection Outcome

Staphylococcus aureus is a common cause of surgical-site infections, including those arising after craniotomy, which is performed to access the brain for the treatment of tumors, epilepsy, or hemorrhage. Craniotomy infection is characterized by complex spatial and temporal dynamics of leukocyte recruitment and microglial activation. We recently identified unique transcriptional profiles of these immune populations during S. aureus craniotomy infection. Epigenetic processes allow rapid and reversible control over gene transcription; however, little is known about how epigenetic pathways influence immunity to live S. aureus. An epigenetic compound library screen identified bromodomain and extraterminal domain-containing (BET) proteins and histone deacetylases (HDACs) as critical for regulating TNF, IL-6, IL-10, and CCL2 production by primary mouse microglia, macrophages, neutrophils, and granulocytic myeloid-derived suppressor cells in response to live S. aureus. Class I HDACs (c1HDACs) were increased in these cell types in vitro and in vivo during acute disease in a mouse model of S. aureus craniotomy infection. However, substantial reductions in c1HDACs were observed during chronic infection, highlighting temporal regulation and the importance of the tissue microenvironment for dictating c1HDAC expression. Microparticle delivery of HDAC and BET inhibitors in vivo caused widespread decreases in inflammatory mediator production, which significantly increased bacterial burden in the brain, galea, and bone flap. These findings identify histone acetylation as an important mechanism for regulating cytokine and chemokine production across diverse immune cell lineages that is critical for bacterial containment. Accordingly, aberrant epigenetic regulation may be important for promoting S. aureus persistence during craniotomy infection.

Molecular mechanisms underlying the clinical efficacy of panobinostat involve Stochasticity of epigenetic signaling, sensitization to anticancer drugs, and induction of cellular cell death related to cellular stresses

Panobinostat, also known as Farydak®, LBH589, PNB, or panobinostat lactate, is a hydroxamic acid that has been approved by the Food and Drug Administration (FDA) for its anti-cancer properties. This orally bioavailable drug is classified as a non-selective histone deacetylase inhibitor (pan-HDACi) that inhibits class I, II, and IV HDACs at nanomolar levels due to its significant histone modifications and epigenetic mechanisms. A mismatch between histone acetyltransferases (HATs) and HDACs can negatively affect the regulation of the genes concerned, which in turn can contribute to tumorigenesis. Indeed, panobinostat inhibits HDACs, potentially leading to acetylated histone accumulation, re-establishing normal gene expression in cancer cells, and helping to drive multiple signaling pathways. These pathways include induction of histone acetylation and cytotoxicity for the majority of tested cancer cell lines, increased levels of p21 cell cycle proteins, enhanced amounts of pro-apoptotic factors (such as caspase-3/7 activity and cleaved poly (ADP-ribose) polymerase (PARP)) associated with decreased levels of anti-apoptotic factors [B-cell lymphoma 2 (Bcl-2) and B-cell lymphoma-extra-large (Bcl-XL)], as well as regulation of immune response [upregulated programmed death-ligand 1 (PD-L1) and interferon gamma receptor 1 (IFN-γR1) expression] and other events. The therapeutic outcome of panobinostat is therefore mediated by sub-pathways involving proteasome and/or aggresome degradation, endoplasmic reticulum, cell cycle arrest, promotion of extrinsic and intrinsic processes of apoptosis, tumor microenvironment remodeling, and angiogenesis inhibition. In this investigation, we aimed to pinpoint the precise molecular mechanism underlying panobinostat's HDAC inhibitory effect. A more thorough understanding of these mechanisms will greatly advance our knowledge of cancer cell aberrations and, as a result, provide an opportunity for the discovery of significant new therapeutic perspectives through cancer therapeutics.

Ginsenoside Rh4 inhibits breast cancer growth through targeting histone deacetylase 2 to regulate immune microenvironment and apoptosis

High expression of histone deacetylase 2 (HDAC2) is recognized as a marker of invasive breast cancer (BC). HDAC2 is not only responsible for enhancing tumor cell growth, development, and anti-apoptosis, but also plays a significant role in regulating PD-L1 on the surface of tumor cells. Continuous expression of PD-L1 allows tumor cells to escape immune surveillance. There is not much research on how HDAC2 affects the immune system in breast cancer. Ginsenoside Rh4 (Rh4) is a major rare saponin in heat-treated ginseng, which is widely applied in treating and preventing various diseases because of its potent medicinal value and stable safety. However, it is unclear how Rh4 affects the tumor immune microenvironment in breast cancer. Therefore, this paper aims to investigate the effect of Rh4 on HDAC2 in breast cancer, specifically the effect of HDAC2 on apoptosis and the immune microenvironment to inhibit breast cancer growth. According to our study, ginsenoside Rh4 has been shown to significantly suppress breast cancer cell proliferation without any adverse effects. The molecular docking results of Rh4 and HDAC2 indicate a binding energy of -6.06 kcal/mol, suggesting the potential of Rh4 as a targeting modulator of HDAC2. Mechanistically, Rh4 induces apoptosis of breast cancer cells by the HDAC2-mediated caspase pathway and inhibits the HDAC2-mediated JAK/STAT pathway to regulate the immune microenvironment, which inhibits breast cancer growth. Specifically, Rh4 was shown for the first time to blockade immune checkpoints (PD-1/PD-L1) and increase levels of T-lymphocytes in the tumor. In a word, our study establishes a theoretical framework for applying Rh4 as an immune checkpoint inhibitor as part of breast cancer treatment.

Epigenomic machinery regulating pediatric AML: clonal expansion mechanisms, therapies, and future perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease with a genetic, epigenetic, and transcriptional etiology mainly presenting somatic and germline abnormalities. AML incidence rises with age but can also occur during childhood. Pediatric AML (pAML) accounts for 15-20% of all pediatric leukemias and differs considerably from adult AML. Next-generation sequencing technologies have enabled the research community to "paint" the genomic and epigenomic landscape in order to identify pathology-associated mutations and other prognostic biomarkers in pAML. Although current treatments have improved the prognosis for pAML, chemoresistance, recurrence, and refractory disease remain major challenges. In particular, pAML relapse is commonly caused by leukemia stem cells that resist therapy. Marked patient-to-patient heterogeneity is likely the primary reason why the same treatment is successful for some patients but, at best, only partially effective for others. Accumulating evidence indicates that patient-specific clonal composition impinges significantly on cellular processes, such as gene regulation and metabolism. Although our understanding of metabolism in pAML is still in its infancy, greater insights into these processes and their (epigenetic) modulation may pave the way toward novel treatment options. In this review, we summarize current knowledge on the function of genetic and epigenetic (mis)regulation in pAML, including metabolic features observed in the disease. Specifically, we describe how (epi)genetic machinery can affect chromatin status during hematopoiesis, leading to an altered metabolic profile, and focus on the potential value of targeting epigenetic abnormalities in precision and combination therapy for pAML. We also discuss the possibility of using alternative epidrug-based therapeutic approaches that are already in clinical practice, either alone as adjuvant treatments and/or in combination with other drugs.

Non-bonding energy directed designing of HDAC2 inhibitors through molecular dynamics simulation

Designing an inhibitor having strong affinity in the active site pocket is the cherished goal of structure based drug designing. To achieve this, it is considerably important to predict which structural scaffold is better suited for change to increase affinity. We have explored five HDAC2 co-crystals having PDB ligand code-SHH (vorinostat), LLX, 20Y, IWX (BRD4884) and 6EZ (BRD7232). For analyzing protein-ligand interaction at an atomistic level, we have employed the NAMD molecular dynamics (MD) package. The obtained 100 ns long MD trajectories were subjected to quantitative estimations of non-bonding energies (NBEs) for inferring their interactions with the whole protein or its composite active site (CAS). In addition, relative ΔG_bind was calculated to rank the inhibitors. These inhibitors' NBEs reveal that the phenyl moieties are the major structural scaffold where modifications should be attempted. We designed new compounds (NCs) via introducing hydroxyl groups at 4,5 position of the phenyl moiety of 6EZ, called NC1. Improvement in NC1 further encouraged us for CAP modification by isochromane and isoindoline moieties in place of oxabicyclooctane in NC1, resulting in NC2 and NC3. We also explored trifluoromethyl oxadiazole in 6EZ (NC4 and NC5) and SHH (NC6 and NC7). This moiety acts as a ZBG in NC4 while acting as a part of the foot-pocket in the rest. NC2 and NC6 have highest favorable NBEs among all studied ligands due increased favorable electrostatic contribution. We expect these NBEs data will provide atomistic level insights and benefit in designing new and improved HDAC2 inhibitors. Communicated by Ramaswamy H. Sarma.

First-in-Class Dual Mechanism Ferroptosis-HDAC Inhibitor Hybrids

HDAC inhibitors are an attractive class of cytotoxic agents for the design of hybrid molecules. Several HDAC hybrids have emerged over the years, but none combines HDAC inhibition with ferroptosis, a combination which is being extensively studied because it leads to enhanced cytotoxicity and attenuated neuronal toxicity. We combined the pharmacophores of SAHA and CETZOLE molecules to design the first-in-class dual mechanism hybrid molecules, which induce ferroptosis and inhibit HDAC proteins. The involvement of both mechanisms in cytotoxicity was confirmed by a series of biological assays. The cytotoxic effects were evaluated in a series of cancer and neuronal cell lines. Analogue HY-1 demonstrated the best cytotoxic profile with GI50 values as low as 20 nM. Although the increase in activity of the hybrids over the combinations is modest in cellular systems, they have the potential advantage of homogeneous spatiotemporal distribution in in vivo systems.

Advances of Epigenetic Biomarkers and Epigenome Editing for Early Diagnosis in Breast Cancer

Epigenetic modifications are known to regulate cell phenotype during cancer progression, including breast cancer. Unlike genetic alterations, changes in the epigenome are reversible, thus potentially reversed by epi-drugs. Breast cancer, the most common cause of cancer death worldwide in women, encompasses multiple histopathological and molecular subtypes. Several lines of evidence demonstrated distortion of the epigenetic landscape in breast cancer. Interestingly, mammary cells isolated from breast cancer patients and cultured ex vivo maintained the tumorigenic phenotype and exhibited aberrant epigenetic modifications. Recent studies indicated that the therapeutic efficiency for breast cancer regimens has increased over time, resulting in reduced mortality. Future medical treatment for breast cancer patients, however, will likely depend upon a better understanding of epigenetic modifications. The present review aims to outline different epigenetic mechanisms including DNA methylation, histone modifications, and ncRNAs with their impact on breast cancer, as well as to discuss studies highlighting the central role of epigenetic mechanisms in breast cancer pathogenesis. We propose new research areas that may facilitate locus-specific epigenome editing as breast cancer therapeutics.

The Role of HDACs in the Response of Cancer Cells to Cellular Stress and the Potential for Therapeutic Intervention

Throughout the process of carcinogenesis, cancer cells develop intricate networks to adapt to a variety of stressful conditions including DNA damage, nutrient deprivation, and hypoxia. These molecular networks encounter genomic instability and mutations coupled with changes in the gene expression programs due to genetic and epigenetic alterations. Histone deacetylases (HDACs) are important modulators of the epigenetic constitution of cancer cells. It has become increasingly known that HDACs have the capacity to regulate various cellular systems through the deacetylation of histone and bounteous nonhistone proteins that are rooted in complex pathways in cancer cells to evade death pathways and immune surveillance. Elucidation of the signaling pathways involved in the adaptive responses to cellular stress and the role of HDACs may lead to the development of novel therapeutic agents. In this article, we overview the dominant stress types including metabolic, oxidative, genotoxic, and proteotoxic stress imposed on cancer cells in the context of HDACs, which guide stress adaptation responses. Next, we expose a closer view on the therapeutic interventions and clinical trials that involve HDACs inhibitors, in addition to highlighting the impact of using HDAC inhibitors in combination with stress-inducing agents for the management of cancer and to overcome the resistance to current cancer therapy.

Recent progress on FAK inhibitors with dual targeting capabilities for cancer treatment

Focal adhesion kinase (FAK, also known as PTK2) is a tyrosine kinase that regulates integrin and growth factor signaling pathways and is involved in the migration, proliferation and survival of cancer cells. FAK is a promising target for cancer treatment. Many small molecule FAK inhibitors have been identified and proven in both preclinical and clinical studies to be effective inhibitors of tumor growth and metastasis. There are many signaling pathways, such as those involving FAK, Src, AKT, MAPK, PI3K, and EGFR/HER-2, that provide survival signals in cancer cells. Dual inhibitors that simultaneously block FAK and another factor can significantly improve efficacy and overcome some of the shortcomings of single-target inhibitors, including drug resistance. In this review, the antitumor mechanisms and research status of dual inhibitors of FAK and other targets, such as Pyk2, IGF-IR, ALK, VEGFR-3, JAK2, EGFR, S6K1, and HDAC2, are summarized, providing new ideas for the development of effective FAK dual-target preparations.

Natural Bioactive Compounds Targeting Histone Deacetylases in Human Cancers: Recent Updates

Cancer is a complex pathology that causes a large number of deaths worldwide. Several risk factors are involved in tumor transformation, including epigenetic factors. These factors are a set of changes that do not affect the DNA sequence, while modifying the gene’s expression. Histone modification is an essential mark in maintaining cellular memory and, therefore, loss of this mark can lead to tumor transformation. As these epigenetic changes are reversible, the use of molecules that can restore the functions of the enzymes responsible for the changes is therapeutically necessary. Natural molecules, mainly those isolated from medicinal plants, have demonstrated significant inhibitory properties against enzymes related to histone modifications, particularly histone deacetylases (HDACs). Flavonoids, terpenoids, phenolic acids, and alkaloids exert significant inhibitory effects against HDAC and exhibit promising epi-drug properties. This suggests that epi-drugs against HDAC could prevent and treat various human cancers. Accordingly, the present study aimed to evaluate the pharmacodynamic action of different natural compounds extracted from medicinal plants against the enzymatic activity of HDAC.

Histone Deacetylases and Their Potential as Targets to Enhance Tumour Radiosensitisation

In mammalian cells, genomic DNA is packaged with histone proteins and condensed into chromatin. To gain access to the DNA, chromatin remodelling is required that is enhanced through histone post-translational modifications, which subsequently stimulate processes including DNA repair and transcription. Histone acetylation is one of the most well understood modifications and is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs). These enzymes play critical roles in normal cellular functioning, and the dysregulation of HDAC expression in particular has been linked with the development of a number of different cancer types. Conversely, tumour cell killing following radiotherapy is triggered through DNA damage and HDACs can help co-ordinate the cellular DNA damage response which promotes radioresistance. Consequently, HDAC inhibitors have been investigated as potential radiosensitizers in vitro and in vivo to improve the efficacy or radiotherapy in specific tumour types. In this review, we provide an up-to-date summary of HDACs and their cellular functions, including in DNA damage repair. We also review evidence demonstrating that HDAC inhibitors can effectively enhance tumour radiosensitisation, and which therefore show potential for translation into the clinic for cancer patient benefit.

Chrysin Modulates Aberrant Epigenetic Variations and Hampers Migratory Behavior of Human Cervical (HeLa) Cells

Purpose: Plant-derived phytochemicals have shown epigenetic modulatory effect in different types of cancer by reversing the pattern of DNA methylation and chromatin modulation, thereby restoring the function of silenced tumor-suppressor genes. In the present study, attempts have been made to explore chrysin-mediated epigenetic alterations in HeLa cells. Methods: Colony formation and migration assays followed by methylation-specific PCR for examining the methylation status of CpG promoters of various tumor-suppressor genes (TSGs) and the expression of these TSGs at the transcript and protein levels were performed. Furthermore, global DNA methylation; biochemical activities of DNA methyltransferases (DNMTs), histone methyl transferases (HMTs), histone deacetylases (HDACs), and histone acetyl transferases (HATs) along with the expression analysis of chromatin-modifying enzymes; and H3 and H4 histone modification marks analyses were performed after chrysin treatment. Results: The experimental analyses revealed that chrysin treatment encourages cytostatic behavior as well as inhibits the migration capacity of HeLa cells in a time- and dose-dependent manner. Chrysin reduces the methylation of various tumor-suppressor genes, leading to their reactivation at mRNA and protein levels. The expression levels of various chromatin-modifying enzymes viz DNMTs, HMTs, HDACs, and HATS were found to be decreased, and H3 and H4 histone modification marks were modulated too. Also, reduced global DNA methylation was observed following the treatment of chrysin. Conclusion: This study concludes that chrysin can be used as a potential epigenetic modifier for cancer treatment and warrants for further experimental validation.

In silico profiling of histone deacetylase inhibitory activity of compounds isolated from Cajanus cajan

Background

Cancer is responsible for high morbidity and mortality globally. Because the overexpression of histone deacetylases (HDACs) is one of the molecular mechanisms associated with the development and progression of some diseases such as cancer, studies are now considering inhibition of HDAC as a strategy for the treatment of cancer. In this study, a receptor-based in silico screening was exploited to identify potential HDAC inhibitors among the compounds isolated from Cajanus cajan, since reports have earlier confirmed the antiproliferative properties of compounds isolated from this plant.

Results

Cajanus cajan-derived phytochemicals were docked with selected HDACs, with givinostat as the reference HDAC inhibitor, using AutodockVina and Discovery Studio Visualizer, BIOVIA, 2020. Furthermore, absorption, distribution, metabolism and excretion (ADME) drug-likeness analysis was done using the Swiss online ADME web tool. From the results obtained, 4 compounds; betulinic acid, genistin, orientin and vitexin, were identified as potential inhibitors of the selected HDACs, while only 3 compounds (betulinic acid, genistin and vitexin) passed the filter of drug-likeness. The molecular dynamic result revealed the best level of flexibility on HDAC1 and HDAC3 compared to the wild-type HDACs and moderate flexibility of HDAC7 and HDAC8.

Conclusions

The results of molecular docking, pharmacokinetics and molecular dynamics revealed that betulinic acid might be a suitable HDAC inhibitor worthy of further investigation in order to be used for regulating conditions associated with overexpression of HDACs. This knowledge can be used to guide experimental investigation on Cajanus cajan-derived compounds as potential HDAC inhibitors.

Epigenetic Mechanisms in Parenchymal Lung Diseases: Bystanders or Therapeutic Targets?

Epigenetic responses due to environmental changes alter chromatin structure, which in turn modifies the phenotype, gene expression profile, and activity of each cell type that has a role in the pathophysiology of a disease. Pulmonary diseases are one of the major causes of death in the world, including lung cancer, idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), pulmonary hypertension (PH), lung tuberculosis, pulmonary embolism, and asthma. Several lines of evidence indicate that epigenetic modifications may be one of the main factors to explain the increasing incidence and prevalence of lung diseases including IPF and COPD. Interestingly, isolated fibroblasts and smooth muscle cells from patients with pulmonary diseases such as IPF and PH that were cultured ex vivo maintained the disease phenotype. The cells often show a hyper-proliferative, apoptosis-resistant phenotype with increased expression of extracellular matrix (ECM) and activated focal adhesions suggesting the presence of an epigenetically imprinted phenotype. Moreover, many abnormalities observed in molecular processes in IPF patients are shown to be epigenetically regulated, such as innate immunity, cellular senescence, and apoptotic cell death. DNA methylation, histone modification, and microRNA regulation constitute the most common epigenetic modification mechanisms.

Improved Anticancer Activities of a New Pentafluorothio-Substituted Vorinostat-Type Histone Deacetylase Inhibitor

The development of new anticancer drugs is necessary in order deal with the disease and with the drawbacks of currently applied drugs. Epigenetic dysregulations are a central hallmark of cancerogenesis and histone deacetylases (HDACs) emerged as promising anticancer targets. HDAC inhibitors are promising epigenetic anticancer drugs and new HDAC inhibitors are sought for in order to obtain potent drug candidates. The new HDAC inhibitor SF5-SAHA was synthesized and analyzed for its anticancer properties. The new compound SF5-SAHA showed strong inhibition of tumor cell growth with IC₅₀ values similar to or lower than that of the clinically applied reference compound vorinostat/SAHA (suberoylanilide hydroxamic acid). Target specific HDAC inhibition was demonstrated by Western blot analyses. Unspecific cytotoxic effects were not observed in LDH-release measurements. Pro-apoptotic formation of reactive oxygen species (ROS) and caspase-3 activity induction in prostate carcinoma and hepatocellular carcinoma cell lines DU145 and Hep-G2 seem to be further aspects of the mode of action. Antiangiogenic activity of SF5-SAHA was observed on chorioallantoic membranes of fertilized chicken eggs (CAM assay). The presence of the pentafluorothio-substituent of SF5-SAHA increased the antiproliferative effects in both solid tumor and leukemia/lymphoma cell models when compared with its parent compound vorinostat. Based on this preliminary study, SF5-SAHA has the prerequisites to be further developed as a new HDAC inhibitory anticancer drug candidate.

A novel HDAC1/2 inhibitor suppresses colorectal cancer through apoptosis induction and cell cycle regulation

Colorectal cancer (CRC) is one of the leading causes of death around the world, and synthetic chemicals targeting specific proteins or various molecular pathways for tumor suppression, such as histone deacetylases (HADC) inhibitors, are under intensively studied. The target of HDAC involves in regulating critical cellular mechanisms and underpins the progression of anticancer therapy. However, little is known about the antitumor mechanisms of class I specific HDAC inhibitors in CRC. We structurally designed and synthesized benzamide-based compounds, examined their anticancer activity in several solid tumors, and identified compound 9 with high potential. Results from the in vitro enzyme and cell-based studies demonstrated that compound 9 as a selective HDAC1/2 inhibitor that possessed short-term and long-term suppression capacities against colorectal cancer cells. Investigation of molecular regulatory mechanisms of 9 in colorectal cancer cells by biological functional assays evidenced that treatment of compound 9 could activate apoptosis, induce cell cycle arrest, facilitate DNA damage process, and suppress cancer migration. A non-cancerous cell line and the in vivo zebrafish model were applied for safety evaluation. In summary, our results demonstrate that compound 9 is a promising lead drug worth further investigation for development of future cancer therapeutic agents.

Roles of HDAC2, eIF5, and eIF6 in Lung Cancer Tumorigenesis

OBJECTIVE

The expression levels of histone deacetylase 2 (HDAC2), eukaryotic initiation factor 5 (eIF5), and eukaryotic initiation factor 6 (eIF6), and relationship between HDAC2 and eIF5 or eIF6 in lung cancer tissues were investigated, in order to charify the relationship between HDAC2 and the prognosis of lung cancer patients and its influence on the expression of eIF5 and eIF6.

METHODS

The expression of HDAC2, eIF5, and eIF6 in lung cancer tissues was detected by quantitative reverse transcription polymerase chain reaction. The expression correlation between HDAC2 and eIF5 or eIF6 was tested using a t test. The correlation between HDAC2 and eIF5 or eIF6 was analyzed using the TCGA database. The identified cells were constructed with small interfering siRNA and HDAC2 overexpression plasmid. The proliferation and migration ability of the identified cells was investigated by CCK8 and Transwell assays, respectively.

RESULTS

HDAC2, eIF5, and eIF6 were overexpressed in lung cancer tissues, and HDAC2 expression level was negatively correlated with the prognosis of lung cancer patients. HDAC2 expression level was positively correlated with eIF5 and eIF6 expression levels. HDAC2 could regulate the expression of eIF5 and eIF6. The regulation of proliferation and invasion of lung cancer cells by HDAC2 depended on eIF5 and eIF6.

CONCLUSION

HDAC2, eIF5, and eIF6 were closely related with lung cancer tumorigenesis, which might be potential biological markers and therapeutic targets for lung cancer.

Anticancer Activity and Mechanisms of Action of New Chimeric EGFR/HDAC-Inhibitors

New chimeric inhibitors targeting the epidermal growth factor (EGFR) and histone deacetylases (HDACs) were synthesized and tested for antineoplastic efficiency in solid cancer (prostate and hepatocellular carcinoma) and leukemia/lymphoma cell models. The most promising compounds, 3BrQuin-SAHA and 3ClQuin-SAHA, showed strong inhibition of tumor cell growth at one-digit micromolar concentrations with IC₅₀ values similar to or lower than those of clinically established reference compounds SAHA and gefitinib. Target-specific EGFR and HDAC inhibition was demonstrated in cell-free kinase assays and Western blot analyses, while unspecific cytotoxic effects could not be observed in LDH release measurements. Proapoptotic formation of reactive oxygen species and caspase-3 activity induction in PCa and HCC cell lines DU145 and Hep-G2 seem to be further aspects of the modes of action. Antiangiogenic potency was recognized after applying the chimeric inhibitors on strongly vascularized chorioallantoic membranes of fertilized chicken eggs (CAM assay). The novel combination of two drug pharmacophores against the EGFR and HDACs in one single molecule was shown to have pronounced antineoplastic effects on tumor growth in both solid and leukemia/lymphoma cell models. The promising results merit further investigations to further decipher the underlying modes of action of the novel chimeric inhibitors and their suitability for new clinical approaches in tumor treatment.

Upregulated histone deacetylase 2 gene correlates with the progression of oral squamous cell carcinoma

BACKGROUND

Histone deacetylases (HDACs) are considered as an essential regulator of cellular proliferation, differentiation, and apoptosis. The HDAC2 enzyme of Class I HDACs plays an important role in tumor progression of human malignancies.

OBJECTIVE

The aim of the present study was to analyze the HDAC2 gene expression in pre-oral cancer and oral squamous cell carcinoma (OSCC), and its association with clinico-pathological features.

METHODS

The HDAC2 protein expression was analyzed through the immunohistochemistry and western blot techniques in 82 oral pre-malignant, 90 OSCC, and 16 normal control tissues. qRT-PCR was used to quantify the mRNA fold change in all groups.

RESULTS

The HDAC2 protein and mRNA levels were significantly higher in OSCC and pre-oral cancer groups compared to the controls. Immunostaining of HDAC2 protein was enhanced in 84.4% of OSCC and 67.1% of pre-cancerous tissue sections (p< 0.01). The mean protein level was analyzed as 1.96 ± 0.44 in oral carcinoma, 1.61 ± 0.39 in pre-cancer and 0.96 ± 0.10 in control tissues. In addition, HDAC2 mean protein level was associated with histological differentiation (OR = 25, p< 0.05) and tumor-node-metastasis (TNM) stages (OR = 6.2, p< 0.05) of OSCC patients.

CONCLUSIONS

The upregulated HDAC2 gene in pre-cancer and OSCC tissues indicates its crucial role in the transformation of pre-malignant to malignant carcinoma. It could be a potential cancer biomarker of prognosis and targeted therapy in OSCC.

Role of Virus-Induced Host Cell Epigenetic Changes in Cancer

The tumor viruses human T-lymphotropic virus 1 (HTLV-1), hepatitis C virus (HCV), Merkel cell polyomavirus (MCPyV), high-risk human papillomaviruses (HR-HPVs), Epstein-Barr virus (EBV), Kaposi’s sarcoma-associated herpes virus (KSHV) and hepatitis B virus (HBV) account for approximately 15% of all human cancers. Although the oncoproteins of these tumor viruses display no sequence similarity to one another, they use the same mechanisms to convey cancer hallmarks on the infected cell. Perturbed gene expression is one of the underlying mechanisms to induce cancer hallmarks. Epigenetic processes, including DNA methylation, histone modification and chromatin remodeling, microRNA, long noncoding RNA, and circular RNA affect gene expression without introducing changes in the DNA sequence. Increasing evidence demonstrates that oncoviruses cause epigenetic modifications, which play a pivotal role in carcinogenesis. In this review, recent advances in the role of host cell epigenetic changes in virus-induced cancers are summarized.

Human papillomavirus E6 and E7: What remains?

Decades of research on the human papillomavirus oncogenes, E6 and E7, have given us huge amounts of data on their expression, functions and structures. We know much about the very many cellular proteins and pathways that they influence in one way or another. However, much of this information is quite discrete, referring to one activity examined under one condition. It is now time to join the dots to try to understand a larger picture: how, where and when do all these interactions occur... and why? Examining these questions will also show how many of the yet obscure cellular processes work together for cellular and tissue homeostasis in health and disease.

A first-in-class anticancer dual HDAC2/FAK inhibitors bearing hydroxamates/benzamides capped by pyridinyl-1,2,4-triazoles

Novel 5-pyridinyl-1,2,4-triazoles were designed as dual inhibitors of histone deacetylase 2 (HDAC2) and focal adhesion kinase (FAK). Compounds 5d, 6a, 7c, and 11c were determined as potential inhibitors of both HDAC2 (IC₅₀ = 0.09-1.40 μM) and FAK (IC₅₀ = 12.59-36.11 nM); 6a revealed the highest activity with IC₅₀ values of 0.09 μM and 12.59 nM for HDAC2 and FAK, respectively. Compound 6a was superior to reference drugs vorinostat and valproic acid in its ability to inhibit growth/proliferation of A-498 and Caki-1 renal cancer cells. Further investigation proved that 6a strongly arrests the cell cycle at the G2/M phase and triggers apoptosis in both A-498 and Caki-1 cells. Moreover, the enhanced Akt activity that is observed upon chronic application of HDAC inhibitors was effectively suppressed by the dual HDAC2/FAK inhibitor. Finally, the high potency and selectivity of 6a towards HDAC2 and FAK proteins were rationalized by molecular docking. Taken together, these findings highlight the potential of 6a as a promising dual-acting HDAC2/FAK inhibitor that could benefit from further optimization.

Structure-activity relationship and mechanistic studies for a series of cinnamyl hydroxamate histone deacetylase inhibitors

Histone deacetylases (HDACs) are a family of enzymes that modulate the acetylation status histones and non-histone proteins. Histone deacetylase inhibitors (HDACis) have emerged as an alternative therapeutic approach for the treatment of several malignancies. Herein, a series of urea-based cinnamyl hydroxamate derivatives is presented as potential anticancer HDACis. In addition, structure-activity relationship (SAR) studies have been performed in order to verify the influence of the linker on the biological profile of the compounds. All tested compounds demonstrated significant antiproliferative effects against solid and hematological human tumor cell lines. Among them, 11b exhibited nanomolar potency against hematological tumor cells including Jurkat and Namalwa, with IC₅₀ values of 40 and 200 nM, respectively. Cellular and molecular proliferation studies, in presence of compounds 11a-d, showed significant cell growth arrest, apoptosis induction, and up to 43-fold selective cytotoxicity for leukemia cells versus non-tumorigenic cells. Moreover, compounds 11a-d increased acetylated α-tubulin expression levels, which is phenotypically consistent with HDAC inhibition, and indirectly induced DNA damage. In vitro enzymatic assays performed for 11b revealed a potent HDAC6 inhibitory activity (IC₅₀: 8.1 nM) and 402-fold selectivity over HDAC1. Regarding SAR analysis, the distance between the hydroxamate moiety and the aromatic ring as well as the presence of the double bond in the cinnamyl linker were the most relevant chemical feature for the antiproliferative activity of the series. Molecular modeling studies suggest that cinnamyl hydroxamate is the best moiety of the series for binding HDAC6 catalytic pocket whereas exploration of Ser568 by the urea connecting unity (CU) might be related with the selectivity observed for the cinnamyl derivatives. In summary, cinnamyl hydroxamate derived compounds with HDAC6 inhibitory activity exhibited cell growth arrest and increased apoptosis, as well as selectivity to acute lymphoblastic leukemia cells. This study explores interesting compounds to fight against neoplastic hematological cells.

GPR126 regulates colorectal cancer cell proliferation by mediating HDAC2 and GLI2 expression

The G‐protein‐coupled receptor 126 (GPR126) may play an important role in tumor development, although its role remains poorly understood. We found that GPR126 had higher expression in most colorectal cancer cell lines than in normal colon epithelial cell lines, and higher expression levels in colorectal cancer tissues than in normal adjacent colon tissues. GPR126 knockdown induced by shRNA inhibited cell viability and colony formation in HT‐29, HCT116, and LoVo cells, decreased BrdU incorporation into newly synthesized proliferating HT‐29 cells, led to an arrest of cell cycle progression at the G1 phase in HCT‐116 and HT‐29 cells, and suppressed tumorigenesis of HT‐29, HCT116, and LoVo cells in nude mouse xenograft models. GPR126 knockdown engendered decreased transcription and translation of histone deacetylase 2 (HDAC2), previously implicated in the activation of GLI1 and GLI2 in the Hedgehog signaling pathway. Ectopic expression of HDAC2 in GPR126‐silenced cells restored cell viability and proliferation, GLI2 luciferase reporter activity, partially recovered GLI2 expression, and reduced the cell cycle arrest. HDAC2 regulated GLI2 expression and, along with GLI2, it bound to the PTCH1 promoter, as evidenced by a chip assay with HT‐29 cells. Purmorphamine, a hedgehog agonist, largely restored the cell viability and expression of GLI2 proteins in GPR126‐silenced HT‐29 cells, whereas GANT61, a hedgehog inhibitor, further enhanced the GPR126 knockdown‐induced inhibitory effects. Our findings demonstrate that GPR126 regulates colorectal cancer cell proliferation by mediating the expression of HDAC2 and GLI2, therefore it may represent a suitable therapeutic target for colorectal cancer treatment.

Histone deacetylase 2: A potential therapeutic target for cancer and neurodegenerative disorders

Histone deacetylases (HDACs) have been implicated in a number of diseases including cancer, cardiovascular disorders, diabetes mellitus, neurodegenerative disorders and inflammation. For the treatment of epigenetically altered diseases such as cancer, HDAC inhibitors have made a significant progress in terms of development of isoform selective inhibitiors. Isoform specific HDAC inhibitors have less adverse events and better safety profile. A HDAC isoform i.e., HDAC2 demonstrated significant role in the development of variety of diseases, mainly involved in the cancer and neurodegenerative disorders. Discovery and development of selective HDAC2 inhibitors have a great potential for the treatment of target diseases. In the present compilation, we have reviewed the role of HDAC2 in progression of cancer and neurodegenerative disorders, and information on the drug development opportunities for selective HDAC2 inhibition.

Histone Deacetylase Inhibitors as Therapeutic Interventions on Cervical Cancer Induced by Human Papillomavirus

The role of epigenetic modifications on the carcinogenesis process has received a lot of attention in the last years. Among those, histone acetylation is a process regulated by histone deacetylases (HDAC) and histone acetyltransferases (HAT), and it plays an important role in epigenetic regulation, allowing the control of the gene expression. HDAC inhibitors (HDACi) induce cancer cell cycle arrest, differentiation, and cell death and reduce angiogenesis and other cellular events. Human papillomaviruses (HPVs) are small, non-enveloped double-stranded DNA viruses. They are major human carcinogens, being intricately linked to the development of cancer in 4.5% of the patients diagnosed with cancer worldwide. Long-term infection of high-risk (HR) HPV types, mainly HPV16 and HPV18, is one of the major risk factors responsible for promoting cervical cancer development. In vitro and in vivo assays have demonstrated that HDACi could be a promising therapy to HPV-related cervical cancer. Regardless of some controversial studies, the therapy with HDACi could target several cellular targets which HR-HPV oncoproteins could be able to deregulate. This review article describes the role of HDACi as a possible intervention in cervical cancer treatment induced by HPV, highlighting the main advances reached in the last years and providing insights for further investigations regarding those agents against cervical cancer.

Cannabinoid Receptor Subtype 2 (CB2R) in a Multitarget Approach: Perspective of an Innovative Strategy in Cancer and Neurodegeneration

The cannabinoid receptor subtype 2 (CB2R) represents an interesting and new therapeutic target for its involvement in the first steps of neurodegeneration as well as in cancer onset and progression. Several studies, focused on different types of tumors, report a promising anticancer activity induced by CB2R agonists due to their ability to reduce inflammation and cell proliferation. Moreover, in neuroinflammation, the stimulation of CB2R, overexpressed in microglial cells, exerts beneficial effects in neurodegenerative disorders. With the aim to overcome current treatment limitations, new drugs can be developed by specifically modulating, together with CB2R, other targets involved in such multifactorial disorders. Building on successful case studies of already developed multitarget strategies involving CB2R, in this Perspective we aim at prompting the scientific community to consider new promising target associations involving HDACs (histone deacetylases) and σ receptors by employing modern approaches based on molecular hybridization, computational polypharmacology, and machine learning algorithms.

Plant flavone Chrysin as an emerging histone deacetylase inhibitor for prosperous epigenetic-based anticancer therapy

Aberrations in epigenetic mechanisms provide a fertile platform for tumour initiation and progression. Thus, agents capable of modulating the epigenetic environment of neoplasms will be a valuable addition to the anticancer therapeutics. Flavones are emerging as befitting anticancer agents due to their inherent antioxidant activity and the ability to restrain epi-targets namely histone deacetylases (HDACs). HDACs have broader implications in pathogenesis of various cancers. Chrysin, a flavone possessing the ability to inhibit HDACs could prove as a potential anticancer drug. Thus, in this article we focussed on Chrysin and its distinct antineoplastic effect against bellicose malignancies including lung, colorectal, cervical, gastric, melanoma, hepatocellular carcinoma and breast cancer. The underlying signalling cascades triggered by Chrysin for inducing cytotoxic effect in these cancer models are discussed. Importantly, approaches towards combinatorial treatments by Chrysin and commercial anticancer agents are taken into account. The downstream molecular mechanism aroused by combined therapy for abrogating onerous cancer chemoresistance is delineated as well. Moreover, the nano-combinatorial approach involving co-encapsulation of Chrysin with other herbal and non-herbal agents for clinical excellence is elucidated.

Histone modifications in epigenetic regulation of cancer: Perspectives and achieved progress

Epigenetic changes associated with histone modifications play an important role in the emergence and maintenance of the phenotype of various cancer types. In contrast to direct mutations in the main DNA sequence, these changes are reversible, which makes the development of inhibitors of enzymes of post-translational histone modifications one of the most promising strategies for the creation of anticancer drugs. To date, a wide variety of histone modifications have been found that play an important role in the regulation of chromatin state, gene expression, and other nuclear events. This review examines the main features of the most common and studied epigenetic histone modifications with a proven role in the pathogenesis of a wide range of malignant neoplasms: acetylation / deacetylation and methylation / demethylation of histone proteins, as well as the role of enzymes of the HAT / HDAC and HMT / HDMT families in the development of oncological pathologies. The data on the relationship between histone modifications and certain types of cancer are presented and discussed. Special attention is devoted to the consideration of various strategies for the development of epigenetic inhibitors. The main directions of the development of inhibitors of histone modifications are analyzed and effective strategies for their creation are identified and discussed. The most promising strategy is the use of multitarget drugs, which will affect multiple molecular targets of cancer. A critical analysis of the current status of approved epigenetic anticancer drugs has also been performed.

Natural Products Impacting DNA Methyltransferases and Histone Deacetylases

Epigenetics refers to heritable changes in gene expression and chromatin structure without change in a DNA sequence. Several epigenetic modifications and respective regulators have been reported. These include DNA methylation, chromatin remodeling, histone post-translational modifications, and non-coding RNAs. Emerging evidence has revealed that epigenetic dysregulations are involved in a wide range of diseases including cancers. Therefore, the reversible nature of epigenetic modifications concerning activation or inhibition of enzymes involved could be promising targets and useful tools for the elucidation of cellular and biological phenomena. In this review, emphasis is laid on natural products that inhibit DNA methyltransferases (DNMTs) and histone deacetylases (HDACs) making them promising candidates for the development of lead structures for anticancer-drugs targeting epigenetic modifications. However, most of the natural products targeting HDAC and/or DNMT lack isoform selectivity, which is important for determining their potential use as therapeutic agents. Nevertheless, the structures presented in this review offer the well-founded basis that screening and chemical modifications of natural products will in future provide not only leads to the identification of more specific inhibitors with fewer side effects, but also important features for the elucidation of HDAC and DNMT function with respect to cancer treatment.

A novel HDAC1 inhibitor, CBUD‑1001, exerts anticancer effects by modulating the apoptosis and EMT of colorectal cancer cells

Colorectal cancer (CRC) is one of the most commonly diagnosed malignancies and is a leading cause of cancer‑related mortality worldwide. Histone deacetylases (HDACs) are a class of enzymes responsible for the epigenetic regulation of gene expression. Some HDAC inhibitors have been shown to be efficient agents for cancer treatment. The aim of the present study was to discover a novel, potent HDAC inhibitor and demonstrate its anticancer effect and molecular mechanisms in CRC cells. A novel fluorinated aminophenyl‑benzamide‑based compound, CBUD‑1001, was designed to specifically target HDAC1, and it was then synthesized and evaluated. CBUD‑1001 exerted a potent inhibitory effect on HDAC enzyme activity and exhibited anticancer potency against CRC cell lines. Molecular docking analysis rationalized the high potency of CBUD‑1001 by validating its conformation in the HDAC active site. Further investigation using CRC cells demonstrated that CBUD‑1001 inhibited HDAC activity by hyper‑acetylating histones H3 and H4, and it exerted an apoptotic effect by activating a mitochondrial‑dependent pathway. Of note, it was found that CBUD‑1001 attenuates the cell motility of CRC cells by downregulating the EMT signaling pathway. Thus, CBUD‑1001 may prove to be a promising novel drug candidate for CRC therapy.

Characterization of Conformationally Constrained Benzanilide Scaffolds for Potent and Selective HDAC8 Targeting

Histone deacetylases (HDACs) are an attractive therapeutic target for a variety of human diseases. Currently, all four FDA-approved HDAC-targeting drugs are nonselective, pan-HDAC inhibitors, exhibiting adverse side effects at therapeutic doses. Although selective HDAC inhibition has been proposed to mitigate toxicity, the targeted catalytic domains are highly conserved. Herein, we describe a series of rationally designed, conformationally constrained, benzanilide foldamers which selectively bind the catalytic tunnel of HDAC8. The series includes benzanilides, MMH371, MMH409, and MMH410, which exhibit potent in vitro HDAC8 activity (IC₅₀ = 66, 23, and 66 nM, respectively) and up to 410-fold selectivity for HDAC8 over the next targeted HDAC. Experimental and computational analyses of the benzanilide structure docked with human HDAC8 enzyme showed the adoption of a low-energy L-shaped conformer that favors HDAC8 selectivity. The conformationally constrained HDAC8 inhibitors present an alternative biological probe for further determining the clinical utility and safety of pharmacological knockdown of HDAC8 in diseased cells.

Clinical significance of HDAC1, -2 and -3 expression levels in esophageal squamous cell carcinoma

The present study analyzed the expression of the histone deacetylase (HDAC) 1, 2 and 3 in primary esophageal squamous cell carcinoma (ESCC) samples and how their levels correlate with clinicopathological parameters. ESCC patients (n=88) in the present study had received no previous treatment before undergoing surgical excision. The mRNA expression of HDAC1, -2 and -3 were detected by semi-quantified PCR in ESCC samples and distal normal samples. The relationship of HDAC1, -2 and -3 expression with clinicopathological parameters was analyzed by χ2 test. The correlation among these HDACs was analyzed by Pearson's correlation test. Compared with distal normal tissues, ESCC samples had higher expression of HDAC1, but not HDAC2 or HDAC3 (P<0.05). The expression of HDACs was different between Kazak and Han ethnicities. The expression of HDAC2 was correlated with invasion depth (P<0.05), but not with sex, age, metastasis, or the degree of tumor differentiation (P>0.05). There was no association between HDAC1 or HDAC3 and clinicopathological parameters (P>0.05). For the Kazak and Han ethnicities, HDAC1 expression was present in male patients, patients with well/moderate differentiated ESCC and T3 and T4 ESCC (P<0.01). HDAC1 in patients aged <60 was associated with ethnicity (P<0.05). HDAC2 expression was different in positive LN metastasis, well/moderate differentiation and T3 and T4 ESCC (P<0.01). HDAC3 expression in male patients, patients with negative LN metastasis and well/moderate differentiation ESCC was associated with ethnicity (P<0.05). Additionally, the expression levels of HDAC1, -2 and -3 did not correlate with each other. Thus, HDAC1 expression may be used as a risk factor for ESCC and HDAC2 levels may be used to predict invasion depth. The expression of HDAC1, -2 and -3 has ethnic differences.

Epigenetic Regulation of the Human Papillomavirus Life Cycle

Persistent infection with certain types of human papillomaviruses (HPVs), termed high risk, presents a public health burden due to their association with multiple human cancers, including cervical cancer and an increasing number of head and neck cancers. Despite the development of prophylactic vaccines, the incidence of HPV-associated cancers remains high. In addition, no vaccine has yet been licensed for therapeutic use against pre-existing HPV infections and HPV-associated diseases. Although persistent HPV infection is the major risk factor for cancer development, additional genetic and epigenetic alterations are required for progression to the malignant phenotype. Unlike genetic mutations, the reversibility of epigenetic modifications makes epigenetic regulators ideal therapeutic targets for cancer therapy. This review article will highlight the recent advances in the understanding of epigenetic modifications associated with HPV infections, with a particular focus on the role of these epigenetic changes during different stages of the HPV life cycle that are closely associated with activation of DNA damage response pathways.

Impact of HDAC Inhibitors on Protein Quality Control Systems: Consequences for Precision Medicine in Malignant Disease

Lysine acetylation is one of the major posttranslational modifications (PTM) in human cells and thus needs to be tightly regulated by the writers of this process, the histone acetyl transferases (HAT), and the erasers, the histone deacetylases (HDAC). Acetylation plays a crucial role in cell signaling, cell cycle control and in epigenetic regulation of gene expression. Bromodomain (BRD)-containing proteins are readers of the acetylation mark, enabling them to transduce the modification signal. HDAC inhibitors (HDACi) have been proven to be efficient in hematologic malignancies with four of them being approved by the FDA. However, the mechanisms by which HDACi exert their cytotoxicity are only partly resolved. It is likely that HDACi alter the acetylation pattern of cytoplasmic proteins, contributing to their anti-cancer potential. Recently, it has been demonstrated that various protein quality control (PQC) systems are involved in recognizing the altered acetylation pattern upon HDACi treatment. In particular, molecular chaperones, the ubiquitin proteasome system (UPS) and autophagy are able to sense the structurally changed proteins, providing additional targets. Recent clinical studies of novel HDACi have proven that proteins of the UPS may serve as biomarkers for stratifying patient groups under HDACi regimes. In addition, members of the PQC systems have been shown to modify the epigenetic readout of HDACi treated cells and alter proteostasis in the nucleus, thus contributing to changing gene expression profiles. Bromodomain (BRD)-containing proteins seem to play a potent role in transducing the signaling process initiating apoptosis, and many clinical trials are under way to test BRD inhibitors. Finally, it has been demonstrated that HDACi treatment leads to protein misfolding and aggregation, which may explain the effect of panobinostat, the latest FDA approved HDACi, in combination with the proteasome inhibitor bortezomib in multiple myeloma. Therefore, proteins of these PQC systems provide valuable targets for precision medicine in cancer. In this review, we give an overview of the impact of HDACi treatment on PQC systems and their implications for malignant disease. We exemplify the development of novel HDACi and how affected proteins belonging to PQC can be used to determine molecular signatures and utilized in precision medicine.

Targeted therapy for mTORC1-driven tumours through HDAC inhibition by exploiting innate vulnerability of mTORC1 hyper-activation

BACKGOUND

The mechanistic target of rapamycin complex 1 (mTORC1) is important in the development and progression of many cancers. Targeted cancer therapy using mTORC1 inhibitors is used for treatment of cancers; however, their clinical efficacies are still limited.

METHODS

We recently created a new mouse model for human lymphangiosarcoma by deleting Tsc1 in endothelial cells and consequent hyper-activation of mTORC1. Using Tsc1iΔEC tumour cells from this mouse model, we assessed the efficacies of histone deacetylase (HDAC) inhibitors as anti-tumour agents for mTORC1-driven tumours.

RESULTS

Unlike the cytostatic effect of mTORC1 inhibitors, HDAC inhibitors induced Tsc1iΔEC tumour cell death in vitro and their growth in vivo. Analysis of several HDAC inhibitors suggested stronger anti-tumour activity of class I HDAC inhibitor than class IIa or class IIb inhibitors, but these or pan HDAC inhibitor SAHA did not affect mTORC1 activation in these cells. Moreover, HDAC inhibitor-induced cell death required elevated autophagy, but was not affected by disrupting caspase-dependent apoptosis pathways. We also observed increased reactive oxygen species and endoplasmic reticulum stress in SAHA-treated tumour cells, suggesting their contribution to autophagic cell death, which were dependent on mTORC1 hyper-activation.

CONCLUSION

These studies suggest a potential new treatment strategy for mTORC1-driven cancers like lymphangiosarcoma through an alternative mechanism.

Roles of Histone Acetylation Modifiers and Other Epigenetic Regulators in Vascular Calcification

Vascular calcification (VC) is characterized by calcium deposition inside arteries and is closely associated with the morbidity and mortality of atherosclerosis, chronic kidney disease, diabetes, and other cardiovascular diseases (CVDs). VC is now widely known to be an active process occurring in vascular smooth muscle cells (VSMCs) involving multiple mechanisms and factors. These mechanisms share features with the process of bone formation, since the phenotype switching from the contractile to the osteochondrogenic phenotype also occurs in VSMCs during VC. In addition, VC can be regulated by epigenetic factors, including DNA methylation, histone modification, and noncoding RNAs. Although VC is commonly observed in patients with chronic kidney disease and CVD, specific drugs for VC have not been developed. Thus, discovering novel therapeutic targets may be necessary. In this review, we summarize the current experimental evidence regarding the role of epigenetic regulators including histone deacetylases and propose the therapeutic implication of these regulators in the treatment of VC.